The invention relates to an underbody stiffening and covering module as well as a motor vehicle underbody.
Reinforcing struts are often installed diagonally on the underbody in motor vehicle bodies in order to reduce twisting during the driving operation, in particular for convertibles, the body stiffness of which is reduced as a consequence of the lack of roof. It is also possible to use struts where an increased tendency for vibration is to be expected. Additional stiffness is thereby targetedly obtained and the individual frequency of the respective body region is increased such that the vibrations take place in a frequency band which is not felt to be disruptive. This relates in particular to regions of the body in which forces and/or torques are applied, so approximately in the region of the storage of the motor/gearbox unit as well as in the region of the wheel drives and/or suspension.
DE 10 2011 009 442 A1 and DE 10 2010 053 346 A1 disclose a motor vehicle underbody reinforced with a diagonal strut device. The diagonal strut device has a number of struts made from a fiber-reinforced material which extend away from a central node, wherein the struts can each be connected to the underbody at their free end via a connection node element which consists of a light metal. The connection node elements can each be connected to the end of the struts positively or via a firm cast connection.
The motor vehicle underbody is frequently clad in order to prevent moisture and dirt influence on the chassis parts and the struts referred to. The underbody covering consists of flat covering parts which each cover a part of the underbody. During the vehicle assembly, the covering parts can only be assembled if chassis parts and reinforcing struts are assembled completely.
Such a covering part is described by DE 195 21 632 A1. This is an injection molded part having comparably thin wall thickness which is produced from an elastic material and is connected to reinforcing struts, which are present on the underbody, on the edge side via screw connections. To connect the covering part to the struts, retaining clips are used which are to prevent the comparably flexible and flat component from sagging.
In order to avoid vibrations and rubbing on the underbody and the struts attached thereto, the underbody covering, with the exception of the fastening or screw-on points, must be attached at a distance to the underbody and to the struts. Important construction space is hereby lost.
Based on this prior art, the object of the present invention is to create an underbody stiffening and covering module with which it is possible, during motor vehicle production, to both stiffen and clad an underbody more quickly and using less assembly material, and to use less construction space.
The underbody stiffening and covering module according to the invention has a flat, non-load-bearing covering component made from a plastic material, to which one or more reinforcing strut(s) is/are connected. The reinforcing strut(s) extends/extend respectively along a predetermined load path and each have a connection device on their end sections, with which it or they, together with the covering component, is or are able to be connected to a predetermined underbody section at force application points.
Firm connections in the sense of the invention are connections in the case of which the connection partners are held together by atomic or molecular forces. They are, at the same time, non-releasable connections which can only be separated by destruction of the connection means.
The reinforcing struts do not serve primarily for the stiffening of the covering component, but rather for the stiffening of a motor vehicle body on the underbody in order to obtain a certain torsional stiffness. The underbody stiffening and covering module according to the invention now combines, however, two functions, in particular the function of the reinforcing struts and the function of the underbody cover, whereby the assembly of a reinforced and clad motor vehicle underbody can be clearly accelerated on the production line and connection means can be saved, since the covering component and the force-conducting reinforcing struts can be attached using the same connection means, for example screws. Furthermore, construction space is saved. The underbody covering must now no longer additionally be at a distance to the reinforcing strut, since the reinforcing strut already represents a part of the underbody covering.
The covering component, or its flat regions, only has to have low mechanical loading capability, since it does not have to transfer any further operational forces apart from the aerodynamic forces and possible forces on contact with obstacles in the road. It can therefore be designed to have very thin walls, for example as a resistant “plastic skin.” The load path is determined based on certain stiffness boundary conditions for the respective underbody to be reinforced; the same load paths as have previously already been reinforced with struts on an existing underbody can also be used. The struts can be both tension struts and pressure struts, wherein the strut cross-section can be optimized with regard to the respective loading type to be expected in order to obtain higher security against buckling.
In a further embodiment, the covering component can have two or more layers between which the reinforcing strut is embedded. The layers abut onto each other in a contract region in which the reinforcing strut is not present, and are firmly connected.
One of the layers is an aurally active layer, for example a layer having a predetermined porosity or having chambers of a predetermined size, which is dimensioned for damping certain frequencies. This layer can be embedded particularly advantageously between two loadable layers which protect the aurally active layer. The aurally active layer is preferably formed from a polymer foam. The foam material can be divided into several chambers. A sandwich structure hereby advantageously results having a core layer made from damping material and/or a reinforcing strut and cover layers, or outer layers, made from loadable plastic. The outer layers can here be designed to have very thin walls, wherein this can be, for example, a loadable plastic film. The aurally active layer here does not have to be fully present between the two “cover layers,” but can also only be arranged locally therebetween in order to achieve improved noise damping locally.
According to a further embodiment, the underbody stiffening and covering module can have at least a further reinforcing strut which extends along a further predetermined load path. The reinforcing strut and the further reinforcing strut can intersect and be connected to each other at the intersection point.
According to the invention, an advantageous embodiment of the invention has more than two struts, which can extend virtually in the manner of a network or a spider web through the underbody stiffening and covering module. The underbody of a motor vehicle body can hereby be targetedly stiffened in several directions, whereby the struts can have an adapted cross-section depending on the forces to be transferred via the respective load path. The assembly of such underbody stiffening and covering modules which are “stiffened multiple times” is not connected to increased expenditure, but rather the assembly course corresponds substantially to the attachment of a usual underbody cover. The underbody covering module can here be flat or even arched or bent. Preferably the bend points of the underbody covering module are present at the ends or the edges of the reinforcing struts such that the reinforcing struts themselves run in a straight line without bend points.
Additionally, the covering component can have one or more channel(s) for embedding the reinforcing strut, into which the reinforcing strut(s) is/are inserted, wherein the cross-section of the channel(s) corresponds advantageously to the cross-section of the reinforcing strut(s) and the reinforcing strut is connected firmly to the channel.
Advantageously, the covering component can be composed of two half-shells, of which each has a channel, which are arranged opposite each other and which together virtually form a “receiving channel” for the reinforcing struts. The reinforcing struts can, with these half-shells, for example, be cast with a plastic casting compound or a glue, whereby the penetration of moisture/dirt into the reinforcing strut can also then be prevented if one of the layers or a half-shell, for example, is damaged by contact with a foreign body.
Finally, the connection device to the underbody can be a bore which extends through the reinforcing strut and the covering component. Alternatively or additionally, the reinforcing strut can have a hollow cross-section. The reinforcing strut can have a circular, rectangular, elliptical or polygonal cross-section. Preferably, the reinforcing strut consists of a fiber-reinforced plastic (FRP), in particular of a carbon fiber-reinforced plastic (CRP).
The bore advantageously extends through all layers of the covering component and through the reinforcing strut itself such that a screw or another connection means can be inserted through. In an advantageous embodiment, the hollow cross-section of the strut can also be filled with an aurally active material, for example can be foamed. In one embodiment, a socket made from an elastomer can be set into the bore in order to achieve, similarly to chassis parts, a flexible connection of the reinforcing strut to the underbody.
A preferred production method for the underbody stiffening and covering module includes the following steps: (a) providing the flat covering component and the at least one reinforcing strut, and (b) positioning the at least one reinforcing strut on the flat covering component at least along the predetermined load path and firmly connecting the reinforcing strut to the flat covering component.
In another embodiment, the following can be executed: in step (a), providing the at least two layers, and in step (b), insertion of the reinforcing strut into the channel of one of the layers, then arranging the other layer on top.
In step (b), a thermoforming step can furthermore be executed in order to connect the reinforcing strut firmly to the covering component. Thermoforming is known from the production of covering parts, wherein a thermoforming system can be modified with low expenditure for the production of the underbody stiffening and covering module according to the invention. The reinforcing strut(s), together with the layer(s) of the covering component, are, for this purpose, inserted into the latter before closing the molding tool, wherein the covering component or the layers of the covering component melt with the reinforcing strut(s) due to heat influence, or a melt adhesive can be used.
The motor vehicle underbody according to the invention has a covering which is connected to an underbody section and has one or more reinforcing strut(s), wherein the covering and the reinforcing strut(s) are provided by an underbody stiffening and covering module according to the invention, wherein the underbody covering part and the reinforcing strut of the underbody stiffening and covering module are connected to common force application points of the underbody section. The load path or the load paths along which the reinforcing strut(s) run here connect the force application points such that the underbody section is stiffened between the force application points. In order to achieve a comprehensive and multi-axis stiffening, an underbody stiffening and covering module is advantageously used having a plurality of reinforcing struts on different load paths. In the case of the underbody according to the invention, defective reinforcing struts and/or connection devices can be exchanged more easily than before, since the covering does not have to be removed first, but rather the respective reinforcing struts can be removed and exchanged as one unit together with the covering component.
For the assembly of the motor vehicle underbody according to the invention, at least the following steps are executed: (a) providing the underbody section and the underbody stiffening and covering module, (b) positioning the underbody stiffening and covering module on the underbody section such that the connection devices of the reinforcing strut of the underbody stiffening and covering module lie over the force application points of the underbody section, and (c) connecting the connection devices of the underbody stiffening and covering module to the force application points of the underbody section, simultaneously thereby fastening the non-load-bearing flat covering component and reinforcing strut to the underbody section.
The advantage which is achieved by using the underbody stiffening and covering module according to the invention is that, to attach the covering and the reinforcing struts, only one step must be executed and here only one set of connection means, for example screws, are used. The assembly can therefore occur more quickly, which can clearly lower the production costs of a motor vehicle which has an underbody according to the invention.
These and further advantages are set out by the description below with regard to the enclosed figures. The reference to the figures in the description serves for the facilitated understanding of the subject matter. The figures are only a schematic depiction of one embodiment of the invention.